River accessory

I spotted this on a post lunch mooch by the river (Medway) by the castle. We stood and watched the tide water coming up and in around it. It was fast. In 10 minutes the water moved about 2 yards up to lap all around it in a sort of flanking manoeuvre.

I had to lean over a wall and zoom a bit so I thought it wouldn't be too clear but I can see the shadow, so am pleased.

There were 2 trolleys and half a dozen traffic cones. When the tide is fully in none of them are visible.
It reminded me of an old Flanders & Swan song about people who dump unlikely things in village ponds. 'So watch the wall my darling as the bedstead men go by...'